This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tuberculosis, especially in its multi-drug resistant form and in combination with AIDS, is a serious health threat. The aim of this proposal is to understand three-dimensional organization of the ParB-DNA assembly of the chromosomal segrosome (ParABS) in Mycobacterium tuberculosis. The segrosome is required for plasmid and chromosome segregation in bacteria. It consists of 2 proteins, named ParA and ParB and a set of 14-16 residue palindromic DNA sequences, parS, which are found near the replication origin. ParB polymerize on the parS-proximal chromosomal DNA to form a large nucleoprotein assembly or the partition complex (covering >1 kilobases of DNA) that recruit a number of proteins in several bacteria, including ParA (an ATPase that drives segregation), SMC (chromosome condensation protein), MipZ (cell division site selector) and PopZ (cell-pole organizing factor). Little is known about the three-dimensional organizations of these cellular superstructures, which is addressed in this proposal. Due to multi-domain and multimeric nature, structural characterization of ParB and its complexes is challenging. A full-length chromosomal ParB has never been crystallized before. Architectural organization of the ParB partition complex will be analyzed using solution scattering, which is a stepping-stone to understand how it stimulates ParA activity and functionally interacts with condensins, leading to chromosome segregation and condensation. Solution scattering data with sucrose contrast variation on the ParB-DNA complex obtained from Bio-SAXS station, together with other experimental data (such as Forster resonance energy transfer, X-ray footprinting with mass spectrometry), will assist in building low-resolution model of segrosome organization. Contrast variations will serve to highlight each component in a two-component system within the solution scattering-derived molecular envelope.